The present invention relates, in general, to semiconductor processing methods, and more particularly, to controlling the operation of an epitaxial reactor.
Previously, the semiconductor industry has utilized a variety of methods for controlling epitaxial reactors that are used to grow epitaxial layers on semiconductor wafers. One type of epitaxial reactor, often referred to as a barrel reactor, employs a transparent quartz bell jar wherein the epitaxial deposition is performed. Epitaxial layers are formed by releasing a silicon source gas, such as silane, and a dopant into the bell jar, then heating the bell jar's contents. During the deposition cycle, doped silicon is deposited onto the semiconductor wafers. Additionally, silicon is also deposited onto the bell jar's inner surface. Such a layer of silicon is often referred to as silicon haze. The haze functions as a barrier that reduces radiant energy which is transmitted through the bell jar to the wafers from heating lamps external to the bell jar. In order to maintain a constant wafer temperature, the lamp intensity is increased as the haze thickness increases thereby reducing the lamps' lifetime.
Typically, the haze is removed by detaching the bell jar from the reactor, and etching the bell jar with a wet chemical etch. The wet etch operation is detrimental to the seals that prevent air from entering the bell jar during epitaxial deposition cycles. In addition, reassembling the bell jar to the reactor, and re-calibrating the reactor takes between twelve and eighteen hours thereby lowering the reactor's through-put and increasing the reactor's operating cost.
Accordingly, it is desirable to have a method of controlling an epitaxial reactor that monitors the silicon haze, that detects when the haze should be removed, that prevents initiating an epitaxial deposition cycle when the haze should be removed thereby increasing lamp lifetime, and that maximizes the number of deposition cycles that are performed before a wet etch operation is required.